1. Field of the Invention
This application relates generally to processing substrates. More particularly, this application relates to the deposition of films onto a substrate and equipment configured for the same.
2. Description of the Related Art
As is well known, substrate processing methods and equipment are often employed for semiconductor processing and for the fabrication of integrated circuits, which entails particularly stringent quality demands, but such processing is also employed in a variety of other fields. For example, semiconductor processing techniques are often employed in the fabrication of flat panel displays using a wide variety of technologies and in the fabrication of microelectromechanical systems (MEMS).
A variety of methods are used in substrate processing to deposit materials onto surfaces. For example, one of the most widely used methods in the semiconductor manufacturing industry is chemical vapor deposition (“CVD”), in which atoms or molecules contained in a vapor deposit on a wafer and build up to form a film. However, existing processes tend to produce films that are non-uniform across the surface of a wafer, resulting in lower quality and yield, and thus, higher costs. Uniformity is often sought by adjusting the parameters of the CVD process, such as by controlling the temperature, pressure, and flow rates of the process gases to and across the surface of the wafer substrate. This adjustment of CVD process parameters is known as “tuning.”
In some contexts, it is desirable to deposit selectively within semiconductor windows exposed among fields of different materials, such as field isolation oxide. Selective deposition means that a film, such as silicon, is deposited on a first portion of the surface of the substrate at a greater mean rate than on a second portion of the same surface. Selectivity takes advantage of differential nucleation and/or formation of different crystal morphology during deposition on disparate materials, and typically comprises simultaneous etching and deposition of the material being deposited. The precursor of choice will generally have a tendency to form more rapidly on one surface and less rapidly on another surface. For example, silane will generally nucleate on both silicon oxide and silicon, but there is a longer nucleation phase on silicon oxide. At the beginning of a nucleation stage, discontinuous films on oxide have a high exposed surface area relative to merged, continuous films on silicon. Similarly, the growth on the insulating regions (e.g., silicon oxide) can be amorphous or polycrystalline whereas growth on the semiconductor windows (e.g., silicon) can be epitaxial. Accordingly, an etchant added to the process will have a greater effect upon the poorly nucleating film on the oxide as compared to the more rapidly nucleating film on the silicon. Similarly, an etchant can be more effective against amorphous or polycrystalline growth, whether from a prior deposition or during deposition, than against epitaxial growth. The relative selectivity of a process can thus be improved by tuning the precursor and vapor etchant as discussed above. Typically, a selective deposition process is tuned to produce the highest deposition rate feasible on the window of interest while accomplishing no deposition in the other regions.
Known selective silicon deposition processes include reactants such as silane and hydrochloric acid with a hydrogen carrier gas. Co-owned and co-pending U.S. Patent Application Publication No. U.S. 2006/0234504 A1, entitled “SELECTIVE DEPOSITION OF SILICON-CONTAINING FILMS,” teaches processes that employ trisilane as a silicon source and chlorine gas as an etchant. These selective deposition processes show improved uniformity, purity, deposition speed and repeatability. However, strong exothermic reactions have been observed, potentially leading to premature reactant breakdown, damage to the gas intermixing tank, combustion, and substrate contamination. Other selective deposition chemistries are also subject to excessive reactivity.